Method and apparatus for generating electrical oscillations



Nov. 8, 1932. A. HUND 1,886,815 METHOD AND APPARATUS FOR GENERATINGELECTRICAL OSCILLATIONS Filed March 5, 1929 Patented Nov. 8, 1932PATENT? OFFICE AUGUST HUND, 0F BETI-IESDA, MARYLAND METHOD AND APPARATUSFOR GENERATING ELECTRICAL OSCILLATIONS Application filed March 5, 1929.

My invention relates broadly to a system of generating electricaloscillations and more particularly to a system for generatingoscillations by means of piezo electric effects.

One of the objects of my invention is to provide a method and apparatusfor generating electrical oscillations by piezo electric effects andwithout the employment of an electron tube oscillating circuit.

Another object of my invention is to provide a piezo electric system forgenerating electrical oscillations which may be operated independentlyof an electron tube oscillating circuit heretofore required in the art.

Still another object of my invention is to,

provide a method and apparatus for generating electrical oscillations ofa selected frequency by initially supplying to a piezo electric crystalsystem an alternating current of a frequency which corresponds to thebeat frequency between the natural frequencies existing in a particularpiezo electric crystal element.

A still further object of my invention is to provide a constructoin ofpiezo electric crystal element having a plurality of natural frequencieswherein the crystal is ground to V produce those frequencies having apredetermined beat note therebetween, which beat note may be supplied tothe piezo electric crystal element for deriving a selected frequencyfrom the crystal and producing sustained oscillation without the aids ofan electron tube circuit as heretofore required in the art.

Still another object of my invention is to provide a system forgenerating oscillations from piezo electric crystals wherein alternatingcurrent of commercial frequency may be supplied to a piezo electriccrystal control circuit for deriving from the piezo electric crystalsystem electrical oscillations of high frequency for supply to anydesired form of utilization circuit.

My invention will be more clearly understood from the followingspecification and the accompanying drawing, in which:

Figure 1 is a diagrammatic view illustrating a piezo electric crystalelement ground in accordance with the principles of my in- Serial No.344,563.

vention; Fig. 2 illustrates a piezo electric crystal element ground in adifferent man ner forproducing oscillations in accordance with theprinciples of my invention; Fig.

3 is a diagrammatic circuit arrangement 5 showing the principlesinvolved in the system of my invention; and Fig. 4 illustrates amodified method of driving the piezo electric crystal element ground inaccordance with the principles of my invention.

In carrying out my invention I employ the piezo electric effects ofquartz crystals. It is well-known that piezo electric crystals have theability of sustaining electrical oscillations in an electrical circuit.A piezo electric crystal may vibrate in a plurality of different modesand at a plurality of ifferent frequencies. The crystal may vibrates1multaneously along different axes at different frequencies.

. In the sustaining of electrical osc1l1at1ons a piezoelectric elementexpands and contracts periodically along the different axes thereof andthe energ Y which is generated may be conducted from the piezo electriccrystal element by contact plates which establi sh connection withopposite faces of the piezo electric crystal element. Stresses are setup in the piezo electric crystal element in accordance with thevibration thereof. Poo tentials may be generated by the piezo elec triccrystal element by subjecting the piezo electric crystal element toperiodic pressure changes applied upon the contact plates.

Heretofore, it has been customary to ar- 35 range an electron tubesystem with the input and output circuits of the electron tube systemcoupled for the production of oscillations and then sustain theoscillations thus produced at constant frequency by coopera- 00 relatedas to produce a predetermined beat we frequency. I then arrange anelectrical circuit in such manner that a frequency corresponding to thebeat frequency may be sup plied to the piezo electric crystal element.The resultant effects are that the piezo electric crystal element isdriven at constant frequency for deriving in an associated electricalcircuit a'frequency corresponding to one of the natural frequencies ofthe piezo electrical crystal element.

Referring to the drawing, Figure 1 illustrates a piezo electric crystal10 with an upper contact plate 11 and a lower contact plate 12. Thepiezo electric crystal is ground so that its natural frequency alongaxis 1--1 is related to the natural frequency along axis 22 so as toproduce a predetermined beat frequency. The piezo crystal is connectedin an electrical circuit as shown in Figure 3 where a source ofalternating current from the supply 14 is utilized to impress energyfrom transformer energy 15 upon the piezo electric crystal to contactplates 11 and 12 at a frequency corresponding to the frequencydifference'between the frequencies along the two axes of the crystalrepresented in Figure 1. I provide radio-frequency by-pass condensers 27and 28 connected in shunt with the secondary winding of transformer 15and also in shunt with piezo electric crystal element 10 as, shown.Electrical oscillations are delivered to tuned circuit 16 coupledthrough transformer circuit 17 with the piezo crystal circuit,the'derived frequency being one of the frequencies for which the piezoelectric crystal is ground. This selected frequency is sustained in thecircuit 16, the energy amplified by electron tube amplifier systemrepresented at 17 and delivered to an output circuit having terminalsrepresented at 18.

Instead of grinding the crystal of a size where the major and minor axeshave the de- "sired frequency diflerence, I may grind the crystal instepped formation as represented in Figure 2, where the crystal 10 hasone portion 20 of greater thickness than the adjacent portion 21, thecrystal vibrating along different axes produced by the conjoint effectof the applied beat frequency.

I have found that the beat frequency may be impressed upon the piezocrystal either electrically as shown in Figure-3 or mechanically asrepresented in Figure 4 where the 1 crystal 10 is centered by means of arim mem ber 22 upon a magnetic diaphragm 23 which may be sub ected tothe constant frequency vibration under influence of electromagnets 2 Lexcited from generator25, impressing the beat frequency upon the crystalfor deriving sustained oscillations in the circuit 26. I Theoscillations may be amplified by a suitable electron tube system, but itis unnecessary to connect the piezo crystal in an electron tubeoscillator circuit. The sustained oscillations are maintained at aconstant frequency determined by the natural frequency of the piezocrystal and are stabilized in the associated circuits Without undueinfluence of the electrical circuits upon the crystal frequency.

IVhile I have described my invention in certain of its preferredembodiments, I desire that it be understood that modifications may bemade and that no limitations upon my invention are intended other thanare imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patentof the UnitedStates is as follows e 1. The method of generating high .frequencyoscillations which comprises, subjecting a. piezo electric crystalelement, adapted to sustain oscillations at abeat frequency of itsplurality of natural frequencies, to cyclic variations corresponding tosaid heat fre quency and deriving oscillations of a freural frequenciesof said piezo electric crystal element. 7

3. The method of generating high frequency oscillations which'comprisesvibrating a piezo electric crystal element, adapted to sustainoscillationsv at a beat frequency of its plurality of naturalfrequencies, at a rate corresponding to said. beat frequency andderiving from said piezo electric crystal element sustained oscillationscorresponding to the frequency of one of said'natural fre quencies. .7 ev 4. The method. of producing sustained high frequency oscillationswhich comprises impressing upon a piezoelectric crystal element, adaptedto sustain oscillations at a beat frequency of its plurality of naturalfre:

quencies, electrical impulses at a rate corre sponding to said beatfrequency, and deriving from said piezo electriccrystal elementsustained high frequency oscillations corresponding to one of thenatural frequencies of said piezoelectric crystal element.

5. In a system for producing high frequency oscillations, a piezoelectric crystal element ground to a multiplicity of differing naturalfrequencies, said frequencies differ-v ing from each other by a beatfrequency, means for impressing electrical energy at a ratecorresponding to said beat frequency upon said piezo electric crystalelement, and

means connected with said piezo electric V crystal element for derivingsustained elecllt trical oscillations corresponding to one of thenatural frequencies of said piezo electric crystal element.

6. In a system for generating electrical oscillations, a circuitincluding a piezo-electric crystal having two natural frequencies ofvibration the difference between which is equal to a certain beatfrequency, a source having a frequency equal to said certain beatfrequency, the frequency and operation of said source being independentof said crystal, said source being coupled to said circuit wherebyvoltage of said certain beat frequency is impressed upon said crystal,and a second circuit tuned to one of said natural frequencies, saidsecond circuit being coupled to said first mentioned circuit andoperable to derive therefrom current of the frequency to which it istuned.

In testimony whereof I aifix my signature.

AUGUST HUND.

